While the number of models dedicated to predicting the consequences of alternative resource management strategies has increased, instances in which authors look back at past predictions to learn from discrepancies between these and observed developments are scarce. In the past decades, the French Guiana shrimp fishery has experienced shrimp market globalization and decreasing levels of shrimp recruitment due to environmental changes. In 2006, a bio‐economic model of this fishery was developed to simulate its possible responses to economic and environmental scenarios up to 2016. Here, we compare here these predictions to the observed trajectories. While the number of active vessels corresponds to that which was predicted, the estimated shrimp stock does not. Important driving factors had not been anticipated, including a general strike, natural disasters, and the end of the global financial crisis. These results show the importance of participative approaches involving stakeholders in the co‐construction and shared representation of scenarios. Recommendations for resource managers
Effective fisheries resources management and a fortiori, the capacity of the fisheries to adapt to global change, requires understanding of both ecological and economics dynamics.
The temporal trajectory of the trawling shrimp fisheries has been well monitored, and the decline of both stock and fleet is understood regarding ecological and economic changes: Changes in the environmental conditions of shrimp recruitment, and oil price increase and selling price decrease.
However, our bio‐economic modeling work showed that, even with a good understanding of the dynamics explaining past trajectories, unpredictable events (strike, natural disasters…) have acted as other key driving factors altering the capacity of the model to represent possible futures.
These results led us to recommend a better integration of the expertise of social and political scientists in developing models of bio‐economic systems to increase the quality of scenario predictions, and to argue for more participative approaches involving the stakeholders.
Far-from-equilibrium models of interacting particles in one dimension
are used as a basis for modelling the stock-market
fluctuations. Particle types and their positions are interpreted as
buy and sel orders placed on a price axis in the order book. We
revisit some modifications of well-known models, starting with the
Bak-Paczuski-Shubik model. We look at the four decades old Stigler
model and investigate its variants. One of them is the simplified
version of the Genoa artificial market. The list of studied models is
completed by the models of Maslov and Daniels et al. Generically, in
all cases we
compare the return distribution, absolute return autocorrelation and
the value of the Hurst exponent. It turns out that none of the models
reproduces satisfactorily all the empirical data, but the most promising
candidates for further development are the Genoa artificial market and
the Maslov model with moderate order evaporation. 相似文献
Opinion compromise models can give insight into how groups of individuals may either come to form
consensus or clusters of opinion groups, corresponding to parties. We consider models where randomly
selected individuals interact pairwise. If the opinions of the interacting agents are not within a certain confidence
threshold, the agents retain their own point of view. Otherwise, they constructively dialogue and smooth their
opinions. Persuasible agents are inclined to compromise with interacting individuals. Stubborn individuals slightly
modify their opinion during the interaction. Collective states for persuasible societies include extremist minorities,
which instead decline in stubborn societies. We derive a mean field approximation for the compromise model in stubborn
populations. Bifurcation and clustering analysis of this model compares favorably with Monte Carlo analysis found in
the literature. 相似文献
We investigate the network model of community by Watts, Dodds and Newman (D.J. Watts et al., Science 296, 1302 (2002)) as a hierarchy of groups, each of 5 individuals. A homophily parameter
α controls the probability proportional to exp (-αx) of selection of neighbours
against distance x. The network nodes are endowed with spin-like variables si = ± 1,
with Ising interaction J > 0. The Glauber dynamics is used to investigate the
order-disorder transition. The transition temperature Tc is close to 3.8 for
α < 0.0 and it falls down to zero above this value. The result provides a mathematical
illustration of the social ability to a collective action via weak ties, as discussed
by Granovetter in 1973. 相似文献
The role of optimization is central to economic analysis, particularly in its “neoclassical” phase, since about 1870, and is therefore highly compatible with the impulse behind linear programming (LP), as developed by Dantzig. LP’s stress on alternative activities fits very well with modern economic analysis. The concept of economic equilibrium, properly understood, required the central notion of complementary slackness. so central in LP.
LP was seen as a tool for actual implementation of neoclassical principles precisely at a time when the market was under attack from several directions. The economists Koopmans and Hurwicz played an important role both in stimulating the crucial development of the simplex method and in relating LP to the world of economics.
LP became widely used in national economic planning, particularly for developing countries, and for the study of individual industries, especially the energy sector. The works of Chenery and of Manne are central in these fields.
As respect for the usefulness of the market increased, the emphasis on national planning diminished and was replaced by an emphasis on equilibrium analysis, in which LP still plays a large part in the study of individual sectors, particularly energy. 相似文献